Lithography is often used to form features on a substrate. Generation of smaller features may use shorter wavelengths. Lithography may use, for example, a 157 nm wavelength lithographic light. Light of this wavelength, and other similar short wavelengths e.g. 126 nm, may present new challenges and especially regarding contamination.
With previous generations of lithography, a mask may be cleaned, then inspected, and then covered with a pellicle, then inspected again. However, the illumination with these shorter wavelengths of light may not be able to easily follow this procedure. At the present time, there are few or no materials that can adequately withstand radiation from the lower wavelength (e.g. 157 nm) light. Another problem, however, is that even if a cover could be added, contamination could still exist when the conventional system of cleaning and testing was used.